Engine

ABSTRACT

An engine includes a cylinder internal pressure sensor, a torque sensor, and an engine control device. The cylinder internal pressure sensor detects a cylinder internal pressure. The torque sensor detects an engine load. The engine control device receives a detection result of the cylinder internal pressure sensor and a detection result of the torque sensor. If the load detected by the torque sensor is zero (no load) and the cylinder internal pressure obtained from the detection result of the cylinder internal pressure sensor is greater than or equal to a threshold, the engine control device determines that an abnormality occurs in detection by the torque sensor.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of a national stage application, U.S.Ser. No. 16/316,303, filed on Jan. 8, 2019, pursuant to 35 U.S.C. § 371of International Application No. PCT/JP2017/025198, filed on Jul. 11,2017 which claims priority under 35 U.S.C. § 119 to Japanese PatentApplication No. 2016-137653 filed on Jul. 12, 2016, the disclosures ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a configuration of an engine thatdetects an engine load by a load detector and performs various controls.

BACKGROUND ART

A known engine includes a load measuring instrument for measuring anengine load. Patent Literature 1 (PTL 1) discloses an engine of thistype. The engine of PTL 1 includes an engine control device forcontrolling components of the engine, and the engine control device isconfigured to receive a measurement signal obtained by a load measuringinstrument, such as a watt transducer or a torque sensor, and calculatesa load of an engine device.

CITATION LIST Patent Literature

Japanese Patent Application Laid-Open No. 2015-230000

SUMMARY OF INVENTION Technical Problem

Measuring a load on an engine as described in PTL 1 is essential forappropriate combustion control of the engine. If the engine is drivenwith a failure of the load measuring instrument, excess or deficiency ofan air volume necessary for combustion occurs, which causes degradationof stability of combustion. The configuration of PTL 1, however, doesnot particularly mention the possibility of occurrence of an abnormalityin load detection by the load measuring instrument, and there is a roomfor improvement.

Some aspects of the present invention have been made in view of theforegoing circumstances, and have an object of providing an enginecapable of appropriately determining an abnormality in a load detector.

Solution to Problem and Advantages

Problems to be solved by the invention are as described above, and next,means for solving the problems and advantages thereof will be described.

In an aspect of the invention, an engine having the followingconfiguration is provided. Specifically, the engine includes an intakemanifold, a gas injector, a fuel injection valve, a cylinder internalpressure sensor, a load detector, and a control device. The intakemanifold supplies air into a cylinder. The gas injector injects gaseousfuel to air supplied from the intake manifold and mixes the gaseous fuelwith the air. The fuel injection valve injects liquid fuel to thecylinder. The cylinder internal pressure sensor detects an internalpressure of a cylinder. The load detector detects an engine load. Thecontrol device receives a detection result of the cylinder internalpressure sensor and a detection result of the load detector. The engineis configured to be driven while being switched between a premixedcombustion mode in which the gaseous fuel injected from the gas injectorand mixed with air is caused to flow into a combustion chamber of thecylinder and a diffusion combustion mode in which combustion occurs byinjection of the liquid fuel by the fuel injection valve into thecombustion chamber. If a load detected by the load detector is zero anda cylinder internal pressure obtained by the detection result of thecylinder internal pressure sensor is a threshold or more, the controldevice determines that an abnormality occurs in detection by the loaddetector. If it is determined that an abnormality occurs in detection bythe load detector during driving in the premixed combustion mode, thecontrol device switches from the premixed combustion mode to thediffusion combustion mode.

Accordingly, it is possible to determine whether an abnormality occursin the load detector or not with a simple configuration by using acertain degree of correlation between the cylinder internal pressure andthe engine load. Consequently, an operator can be urged early to copewith an abnormality, for example. In addition, it is possible to preventdriving of the engine in the premixed combustion mode with occurrence ofan abnormality in detection of an engine load by the load detector. As aresult, continuity of driving of the engine can be maintained.

In the engine, if it is determined that an abnormality occurs indetection by the load detector during driving in the premixed combustionmode and the premixed combustion mode is switched to the diffusioncombustion mode, the control device preferably estimates an engine loadbased on a detection value of the cylinder internal pressure sensor bycalculation and, based on the estimated engine load, calculates theamount of the liquid fuel injected by the fuel injection valveimmediately after switching to the diffusion combustion mode.

Accordingly, in an initial stage in which the premixed combustion modeis switched to the diffusion combustion mode, the appropriate amount ofliquid fuel can be injected from the fuel injection valve by using thedetection result of the cylinder internal pressure sensor. Consequently,the engine can be driven stably without degradation of the engine speedin mode switching, for example.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A view schematically illustrating an engine and fuel supply pathsof two systems according to one embodiment of the present invention.

FIG. 2 A partial rear cross-sectional view illustrating a configurationaround a combustion chamber in detail.

FIG. 3 A plan view of the engine.

FIG. 4 A schematic front perspective view illustrating a liquid fuelsupply path.

FIG. 5 A view illustrating a configuration of intake and exhaust systemsof the engine.

FIG. 6 A block diagram illustrating an electric configuration forcontrolling the engine.

FIG. 7 A graph for describing control of adjusting an intake flow ratein an intake manifold when the engine is driven in a gas mode.

FIG. 8 A flowchart depicting a determination process performed by anengine control device for detecting an abnormality in the torque sensor.

FIG. 9 Graphs for describing supply control of fuel gas and fuel oil ina case where a gas mode is switched to a diesel mode as a result ofdetection of an abnormality in the torque sensor.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described with referenceto the drawings. FIG. 1 is a view schematically illustrating an engine21 and fuel supply paths 30 and 31 of two systems according to oneembodiment of the present invention. FIG. 2 is a partial rearcross-sectional view illustrating a configuration around a combustionchamber 110 in detail. FIG. 3 is a plan view of the engine 21. FIG. 4 isa schematic front perspective view illustrating a liquid fuel supplypath.

The engine (multi-cylinder engine) 21 according to this embodimentillustrated in FIG. 1 is a so-called dual fuel engine operable in both apremixed combustion system in which gaseous fuel mixed with air iscaused to flow into combustion chambers and a diffusion combustionsystem that injects liquid fuel into the combustion chambers forcombustion. The engine 21 according to this embodiment is mounted to aninner bottom plate of an engine room of an unillustrated ship with abase interposed therebetween, and serves as a driving source of anunillustrated propulsive and power generating mechanism of the ship.

A crank shaft 24 serving as an engine output shaft projects rearwardfrom a rear end of the engine 21. An unillustrated speed-reducer iscoupled to one end of the crank shaft 24 to enable power transfer. Thespeed reducer is sandwiched between the crank shaft 24 and anunillustrated propeller shaft of the ship, and the propeller shaft isdisposed coaxially with the crank shaft 24. A propeller for generatingpropulsive power of the ship is attached to an end of the propellershaft. The speed-reducer includes a PTO shaft, and an unillustratedshaft-driving power generator is coupled to the PTO shaft to enablepower transfer.

This configuration enables a driving force of the engine 21 to bebranched into the propeller shaft and the shaft-driving power generatorand transferred through the speed-reducer. Accordingly, propulsive powerof the ship is generated, and electric power generated by driving theshaft-driving power generator is supplied to electric circuits in theship.

Next, the engine 21 will be described in detail with reference to thedrawings. The engine 21 is a dual fuel engine as described above, andcan be driven while selecting one of a premixed combustion system inwhich fuel gas such as natural gas is mixed with the air for combustionand a diffusion combustion system in which liquid fuel (fuel oil) suchas heavy oil is diffused for combustion.

In the following description, a driving mode by the premixed combustionsystem (premixed combustion mode) will be sometimes referred to as a“gas mode,” and a driving mode by the diffusion combustion system(diffusion combustion mode) will be sometimes referred to as a “dieselmode.” In the gas mode, environmentally hazardous substances (e.g.,nitrogen oxides, sulfur oxides, and particulate matter) can be reducedby utilizing natural gas, whereas in the diesel mode, highly efficientdriving can be achieved.

Positional relationship among the front, rear, left, and right in theconfiguration of the engine 21 will be described below with a sideconnected to the speed-reducer being defined as a rear side.Accordingly, the front-rear direction (longitudinal direction) can be adirection parallel to the axis of the crank shaft 24, and the left-rightdirection (lateral direction) can be a direction perpendicular to theaxis of the crank shaft 24. It should be noted that this description isnot intended to limit the orientation of the engine 21, and the engine21 can be placed in various orientations in accordance with applicationand others.

As illustrated in FIG. 1, the fuel supply paths of two systems 30 and 31are connected to the engine 21. A gaseous fuel tank 32 for storingliquefied natural gas (LNG) is connected to one fuel supply path 30,whereas a liquid fuel tank 33 for storing a marine diesel oil (MDO) isconnected to the other fuel supply path 31. In this configuration, thefuel supply path 30 supplies fuel gas to the engine 21, and the fuelsupply path 31 supplies fuel oil to the engine 21.

In the fuel supply path 30, a gaseous fuel tank 32 that stores gaseousfuel in a liquefied state, a vaporizing device 34 that vaporizes theliquefied fuel in the gaseous fuel tank 32, and a gas valve unit 35 thatadjusts the supply rate of fuel gas from the vaporizing device 34 to theengine 21, are arranged in this order from the upstream side.

As illustrated in FIGS. 2 and 4, the engine 21 is an in-linemulti-cylinder engine configured by attaching cylinder heads 26 onto acylinder block 25. The crank shaft 24 is rotatably supported on a lowerportion of the cylinder block 25 with an axis 24 c oriented in thefront-rear direction as illustrated FIG. 4.

In the cylinder block 25, a plurality of (six in this embodiment)cylinders are arranged in a line (in series) along the axis of the crankshaft 24. As illustrated in FIG. 2, each cylinder houses a piston 78 sothat the pistons 78 are slidable in the top-bottom direction. Thispiston 78 is coupled to the crank shaft 24 through an unillustrated rod.

As illustrated in FIG. 3, the six cylinder heads 26 are attached to thecylinder block 25 to cover the cylinders individually from above. Thecylinder heads 26 are provided to the individual cylinders, and arefixed to the cylinder block 25 using head bolts 99. As illustrated inFIG. 2, in each cylinder, the combustion chamber 110 is defined in spacesurrounded by the upper surface of the piston 78 and the cylinder head26.

As illustrated in FIG. 3, a plurality of head covers 40 correspond tothe individual cylinders and are arranged on the cylinder heads 26 in aline along the direction of the axis 24 c of the crank shaft 24(front-rear direction). As illustrated in FIG. 2, each of the headcovers 40 houses a valve mechanism constituted by a push rod, a rockerarm, and so forth in order to operate an intake valve and an exhaustvalve. In a state where the intake valves are open, intake air from anintake manifold 67 can be taken in the combustion chambers 110. In astate where the exhaust valves are open, exhaust air from the combustionchambers 110 can be emitted to an exhaust manifold 44.

As illustrated in FIG. 2, the upper end of a pilot fuel injection valve82 described later is disposed near the right of each head cover 40. Thepilot fuel injection valves 82 are inserted in the cylinder heads 26,and extend obliquely downward toward the corresponding combustionchambers 110.

As illustrated in FIG. 2, a gas manifold 41 for distributing andsupplying gaseous fuel to the combustion chambers 110 of the cylindersduring driving in the gas mode (premixed combustion mode) is provided atthe right of the cylinder heads 26. The gas manifold 41 extends in thefront-rear direction along the right side surfaces of the cylinder heads26. Six gas branch pipes 41 a corresponding to the combustion chambers110 of the cylinders are connected to the gas manifold 41, and asillustrated in FIG. 2, gas injectors 98 for injecting gaseous fuel areprovided at the front ends of the gas branch pipes 41 a. The front endsof the gas injectors 98 face intake branch pipes 67 a corresponding tothe cylinders and formed inside the cylinder heads 26. By injectinggaseous fuel from the gas injectors 98, the gaseous fuel can be suppliedto the intake branch pipes 67 a of the intake manifold 67.

As illustrated in FIGS. 2 and 4, a liquid fuel supply rail pipe 42 fordistributing and supplying liquid fuel to the combustion chambers 110 ofthe cylinders during driving in the diesel mode (diffusion combustionmode) is disposed at the left of the cylinder block 25. The liquid fuelsupply rail pipe 42 extends in the front-rear direction along the leftside surface of the cylinder block 25. Liquid fuel supplied to theliquid fuel supply rail pipe 42 is distributed and supplied to fuelsupply pumps 89 corresponding to the cylinders. As illustrated in FIG.2, each cylinder is provided with a main fuel injection valve 79 thatinjects liquid fuel supplied from the fuel supply pump 89. The main fuelinjection valves 79 are inserted in the cylinder heads 26 verticallyfrom above the cylinder heads 26, the upper ends of the main fuelinjection valves 79 are disposed inside the head covers 40, and thelower ends of the main fuel injection valves 79 face the combustionchambers 110 of the cylinders. The fuel supply pumps 89 and the mainfuel injection valves 79 are connected to each other through liquid fuelsupply paths 106 formed in the cylinder heads 26.

A liquid fuel return aggregate pipe 48 for collecting redundant fuelreturned from the fuel supply pumps 89 is disposed near the bottom ofthe liquid fuel supply rail pipe 42. The liquid fuel return aggregatepipe 48 is disposed in parallel with the liquid fuel supply rail pipe42, and connected to the fuel supply pumps 89. A fuel return pipe 115for returning liquid fuel to the liquid fuel tank 33 is connected to anend of the liquid fuel return aggregate pipe 48.

As illustrated in FIGS. 2 and 4, a pilot fuel supply rail pipe 47 fordistributing and supplying pilot fuel to the combustion chambers 110 ofthe cylinders in order to ignite gaseous fuel in combustion in the gasmode (premixed combustion mode) is disposed at the left of the cylinderblock 25 and above the liquid fuel supply rail pipe 42. The pilot fuelsupply rail pipe 47 extends in the front-rear direction along the leftside surface of the cylinder block 25. As illustrated in FIGS. 2 and 4,the cylinders are provided with the pilot fuel injection valves 82 forinjecting liquid fuel (pilot fuel) supplied from the pilot fuel supplyrail pipe 47. The pilot fuel injection valves 82 are inserted in thecylinder heads 26 vertically from above the cylinder heads 26, the upperends of the pilot fuel injection valves 82 are disposed immediately atthe right side of the head covers 40, and the lower ends of the pilotfuel injection valves 82 face the combustion chambers 110 of thecylinders. As illustrated in FIG. 4, pilot fuel branch pipes 109corresponding to the cylinders branch off from the pilot fuel supplyrail pipe 47. The pilot fuel branch pipes 109 pass between the headcovers 40 arranged side by side, and are connected to the upper ends ofthe pilot fuel injection valves 82. The pilot fuel branch pipes 109 arecovered with a branch pipe cover 105 for preventing leaked fuel fromscattering.

As illustrated in FIGS. 2 and 4, a step is formed on an upper portion ofthe left side surface of the engine 21 constituted by the cylinder block25 and the cylinder heads 26. The pilot fuel supply rail pipe 47, theliquid fuel supply rail pipe 42, and the fuel supply pumps 89 aredisposed on this step. A side cover 43 is attached to the cylinder block25 and the cylinder heads 26 to cover the step. The pilot fuel supplyrail pipe 47, the liquid fuel supply rail pipe 42, and the fuel supplypumps 89 are covered with the side cover 43.

As illustrated in FIG. 3, for example, a speed adjuster 201 foradjusting the fuel injection rate of the fuel supply pumps 89 isdisposed near one end in the direction in which the fuel supply pumps 89are arranged. The speed adjuster 201 is capable of rotating a controltransfer shaft 202 disposed in parallel with the liquid fuel supply railpipe 42 and other components inside the side cover 43. The controltransfer shaft 202 is coupled to a control rack of the fuel supply pumps89 in the same number as that of the number of the cylinders. The speedadjuster 201 rotates the control transfer shaft 202 to thereby displacethe control rack of the fuel supply pumps 89 so that the pumping speedof the fuel supply pumps 89 (injection rate of the main fuel injectionvalve 79) can be changed.

As illustrated in FIG. 2, the exhaust manifold 44 for collecting exhaustair generated by combustion in the combustion chambers 110 of thecylinders and emitting the exhaust air to the outside is disposed inparallel with the gas manifold 41 above the right of cylinder heads 26and above the gas manifold 41. The outer periphery of the exhaustmanifold 44 is covered with a heat shielding cover 45. As illustrated inFIG. 2, exhaust branch pipes 44 a corresponding to the cylinders areconnected to the exhaust manifold 44. The exhaust branch pipes 44 acommunicate with the combustion chambers 110 of the cylinders.

The intake manifold 67 for distributing and supplying outside air(intake air) to the combustion chambers 110 of the cylinders is disposedin parallel with the gas manifold 41 inside the cylinder block 25 andnear the cylinder block 25. As illustrated in FIG. 2, the six intakebranch pipes 67 a branching off from the intake manifold 67 are formedinside the cylinder heads 26 and communicate with the individualcombustion chambers 110.

With this configuration, in driving in the diesel mode (diffusioncombustion mode), an appropriate amount of liquid fuel is injected fromthe main fuel injection valves 79 into the combustion chambers 110 at anappropriate timing when air supplied to the cylinders from the intakemanifold 67 is compressed by sliding of the pistons 78. Injection ofliquid fuel into the combustion chambers 110 causes the pistons 78 toreciprocate in the cylinders with propulsive power obtained bycombustion in the combustion chambers 110, and the reciprocatingmovement of the pistons 78 is converted to rotation movement of thecrank shaft 24 through a rod, thereby obtaining a driving force.

On the other hand, in driving in the gas mode (premixed combustionsystem), gaseous fuel from the gas manifold 41 is injected from the gasinjectors 98 into the intake branch pipes 67 a so that air supplied fromthe intake manifold 67 and the gaseous fuel are mixed. At an appropriatetiming when the air mixture of the air introduced into the cylinders andthe gaseous fuel is compressed by sliding of the pistons 78, a smallamount of pilot fuel is injected from the pilot fuel injection valves 82into the combustion chambers 110 so that the gaseous fuel is ignited.The pistons 78 reciprocates in the cylinders with propulsive powerobtained by combustion in the combustion chambers 110, and thereciprocating movement of the pistons 78 is converted to rotationmovement of the crank shaft 24 through the rod, thereby obtaining adriving force.

In either case of driving in the diesel mode and driving in the gasmode, exhaust air generated by combustion is pushed out from thecylinders by movement of the pistons 78, and collected in the exhaustmanifold 44, and then emitted to the outside.

The front end surface (front surface) of the engine 21 is provided witha fuel oil pump 56, an unillustrated cooling water pump, and alubricating oil pump that surround a front end portion of the crankshaft 24. A rotative force is appropriately transferred from the crankshaft 24 so that the cooling water pump, the lubricating oil pump, andthe fuel oil pump 56 provided at the outer periphery of the crank shaft24 are driven.

The fuel oil pump 56 illustrated in FIG. 4 is driven to rotate so thatfuel oil (liquid fuel) supplied from the liquid fuel tank 33 illustratedin FIG. 1 is sent to the pilot fuel supply rail pipe 47 by way of apilot fuel supply main pipe 107. A pilot fuel filter for filtering fueloil is provided in an intermediate portion of a fuel path from theliquid fuel tank 33 to the fuel oil pump 56.

An unillustrated fuel oil pump (different from the fuel oil pump 56) isdriven to rotate with rotation of the crank shaft 24 so that this fuelpump sucks fuel oil from the liquid fuel tank 33, and sends the fuel oilto the liquid fuel supply rail pipe 42 by way of a liquid fuel supplymain pipe 108 illustrated in, for example, FIG. 4. A main fuel filterfor filtering fuel oil is disposed in an intermediate portion of asupply path of fuel oil from the liquid fuel tank 33 to the liquid fuelsupply rail pipe 42.

As illustrated in FIG. 4, the pilot fuel supply main pipe 107, theliquid fuel supply main pipe 108, and the fuel return pipe 115 aredisposed immediately ahead of the cylinder block 25 and extend along theleft side surface of the cylinder block 25. The pilot fuel supply mainpipe 107, the liquid fuel supply main pipe 108, and the fuel return pipe115 extend in the top-bottom direction along the left side surface ofthe cylinder block 25 through a plurality of clamp members 111projecting leftward from the front end surface of the cylinder block 25.

An engine control device (control device) 73 for controlling operationof components of the engine 21 is provided near the right of the rear ofthe cylinder block 25 with an unillustrated support member interposedtherebetween. As illustrated in FIG. 6, the engine control device 73 isconfigured to acquire data from sensors (e.g., a pressure sensor and atorque sensor) provided in components of the engine 21 and controloperations (e.g., fuel injection and change of the opening degree of theflow-rate control valve) of the engine 21.

Next, a configuration for intaking and exhausting air in the engine 21will be described with reference to FIG. 5. FIG. 5 is a schematic viewillustrating a configuration of intake and exhaust systems of the engine21.

As illustrated in FIG. 5, six cylinders are arranged in a line in theengine 21. Each cylinder is connected to the intake manifold 67 throughthe intake branch pipe 67 a, and connected to the exhaust manifold 44through the exhaust branch pipe 44 a.

The intake manifold 67 is connected to an intake channel 15communicating with the outside of the engine 21 to be capable of takingoutside air into the cylinders. A compressor 49 b of a turbocharger 49and an intercooler 51 are disposed in an intermediate portion of theintake channel 15.

A main throttle valve V1 for adjusting the flow rate of air supplied tothe intake manifold 67 is disposed between the compressor 49 b and theintercooler 51. The main throttle valve V1 is configured as a flow-ratecontrol valve, and is configured to enable control of the opening degreeof the valve based on an electrical signal from the engine controldevice 73.

The intake channel 15 is provided with an intake bypass channel 17connecting an air outlet of the intercooler 51 and an air inlet of thecompressor 49 b. A part of air that has passed through the compressor 49b is circulated again by way of the intake bypass channel 17. The intakebypass channel 17 is provided with an intake bypass valve V2 foradjusting the flow rate of air passing through the intake bypass channel17. The intake bypass valve V2 is configured as a flow-rate controlvalve in a manner similar to the main throttle valve V1, and isconfigured such that the opening degree of the intake bypass valve V2 iscontrollable based on an electrical signal from the engine controldevice 73. By changing the opening degree of the intake bypass valve V2,the flow rate of air supplied to the intake manifold 67 can be adjusted.

The exhaust manifold 44 is connected to an exhaust channel 16communicating with the outside of the engine 21 and is capable ofemitting air from the cylinders to the outside. A turbine 49 a of theturbocharger 49 is disposed in an intermediate portion of the exhaustchannel 16.

The exhaust channel 16 is provided with an exhaust bypass channel 18connecting an exhaust outlet of the exhaust manifold 44 and an exhaustoutlet of the turbine 19 a (bypassing the turbine 19 a). A part ofexhaust air sent from the exhaust manifold 44 to the exhaust channel 16reaches a portion downstream of the exhaust outlet of the turbine 49 aby way of the exhaust bypass channel 18 and is emitted to the outside.The exhaust bypass channel 18 is provided with an exhaust bypass valveV3 for adjusting the flow rate of exhaust air passing through theexhaust bypass channel 18. The exhaust bypass valve V3 is configured asa flow-rate control valve in a manner similar to the main throttle valveV1, and is configured such that the opening degree of the intake bypassvalve V3 is controllable based on an electrical signal from the enginecontrol device 73. The flow rate of exhaust air flowing into the turbine49 a is adjusted by changing the valve opening degree of the exhaustbypass valve V3 so that the compression amount of air in the compressor49 b can be adjusted. That is, the flow rate of air supplied to theintake manifold 67 can be adjusted by adjusting the valve opening degreeof the exhaust bypass valve V3.

Next, feedback control in the valve opening degree of the flow-ratecontrol valve will be described with reference to FIGS. 6 and 7. FIG. 6is a block diagram illustrating an electric configuration forcontrolling the engine 21. FIG. 7 is a graph for describing control ofadjusting an intake flow rate in the intake manifold 67 when the engine21 is driven in the gas mode.

As illustrated in FIG. 6, the engine control device 73 is configured tocontrol the pilot fuel injection valves 82, the fuel supply pumps 89,and the gas injectors 98. The engine control device 73 controls openingand closing of the pilot fuel injection valves 82 to supply liquid fuel(pilot fuel) to the combustion chambers 110. The engine control device73 controls opening and closing of the control valve of the fuel supplypumps 89 to thereby supply liquid fuel (main fuel) from the fuel supplypumps 89 to the combustion chambers 110 through the main fuel injectionvalves 79. The engine control device 73 controls the speed adjuster 201to thereby adjust the injection amount of liquid fuel from the main fuelinjection valves 79. The engine control device 73 can supply gaseousfuel to the intake branch pipes 67 a of the intake manifold 67 bycontrolling the gas injectors 98.

The engine control device 73 is configured to control the main throttlevalve V1, the intake bypass valve V2, and the exhaust bypass valve V3.As described above, the engine control device 73 controls the openingdegrees of the main throttle valve V1, the intake bypass valve V2, andthe exhaust bypass valve V3 to thereby adjust the flow rate of airflowing into the intake manifold 67.

As illustrated in FIG. 6, the engine control device 73 is configured toreceive signals from the sensors provided in components of the engine21. The engine control device 73 is configured to communicate with anengine-side operation control device 71.

Cylinder internal pressure sensors 63 are disposed in a part or thewhole of six cylinders of the engine 21. Each of the cylinder internalpressure sensors 63 includes a piezoelectric element or a strain gauge,for example, and is capable of detecting an internal pressure of thecylinder (illustrated mean effective pressure, IMEP). The internalpressures of the cylinder detected by the cylinder internal pressuresensors 63 are output to the engine control device 73.

The intake manifold 67 of the engine 21 is provided with an intakepressure sensor 39 for measuring an air pressure in the intake manifold67. This intake pressure sensor 39 can be configured using asemiconductor strain gauge, for example, The intake pressure detected bythe intake pressure sensor 39 is output to the engine control device 73.

A torque sensor (load detector) 64 is attached to an appropriatelocation (e.g., near the crank shaft 24) of the engine 21. Examples ofthe torque sensor 64 include a flange-type sensor for detecting a torqueusing a strain gauge. An engine load (engine torque) detected by thetorque sensor 64 is output to the engine control device 73.

An engine speed sensor 65 is attached to an appropriate location (e.g.,the cylinder block 25) of the engine 21. The engine speed sensor 65 isconstituted by, for example, a sensor and a sensor pulse generator, andcan be configured to generate a pulse signal in accordance with rotationof the crank shaft 24. The engine speed detected by the engine speedsensor 65 is output to the engine control device 73.

In driving the engine 21 in the diesel mode, the engine control device73 controls opening and closing of the control valves in the fuel supplypumps 89 to cause combustion in the cylinders at a predetermined timing.That is, the control valves of the fuel supply pumps 89 are opened inaccordance with the injection timings of the cylinders so that fuel oilis injected into the cylinders through the main fuel injection valves79, and combustion occurs in the cylinders. On the other hand, injectionof fuel gas from the gas injectors 98 and injection of pilot fuel fromthe pilot fuel injection valves 82 are suspended in the diesel mode.

In the diesel mode, the engine control device 73 performs feedbackcontrol on the timing of injection from the main fuel injection valve 79in each cylinder based on the engine load detected by the torque sensor64 and the engine speed detected by the engine speed sensor 65.Accordingly, the crank shaft 24 of the engine 21 rotates at an enginespeed in accordance with a propulsion speed of the ship so as to obtaina torque necessary for the propulsive and power generating mechanism ofthe ship. The engine control device 73 controls the valve opening degreeof the main throttle valve V1 based on an air pressure in the intakemanifold 67 detected by the intake pressure sensor 39. Accordingly,compressed air is supplied from the compressor 49 b to the intakemanifold 67 so as to obtain an airflow rate necessary for an engineoutput.

In the case of driving the engine 21 in the gas mode, the engine controldevice 73 controls opening and closing of the valves in the gasinjectors 98 to supply fuel gas to the intake branch pipes 67 a, therebymixing the fuel gas with air from the intake manifold 67 and supplyingpremixed fuel to the cylinders. The engine control device 73 alsocontrols opening and closing of the pilot fuel injection valves 82 andinjects pilot fuel to the cylinders at a predetermined timing to therebygenerate an ignition source so that combustion is performed in thecylinders supplied with the premixed gas. On the other hand, injectionof main fuel from the main fuel injection valve 79 is suspended in thegas mode.

In the gas mode, the engine control device 73 performs feedback controlon the injection flow rate of fuel gas by the gas injectors 98 and thetiming of injection from the pilot fuel injection valves 82, based onthe engine load detected by the torque sensor 64 and the engine speeddetected by the engine speed sensor 65.

Based on the engine load detected by the torque sensor 64, the airpressure in the intake manifold 67 detected by the intake pressuresensor 39, and so forth, the engine control device 73 controls the valveopening degrees of the main throttle valve V1, the intake bypass valveV2, and the exhaust bypass valve V3, as illustrated in FIG. 7, forexample.

First, control of the main throttle valve V1 will be described withreference to FIG. 7(a). In the graph of FIG. 7, L1, L2, L3, and L4 arepredetermined specific values of the engine load (where L1<L2<L3<L4),and the specific value L4 is an engine load corresponding to theboundary between a low-load region and an intermediate and high-loadregions.

If the engine load is less than the specific value L1, the enginecontrol device 73 sets a target pressure of the intake manifold 67 inaccordance with the engine load based on the relationship shown in FIG.7(d), and then performs PID control (feedback control) on the valveopening degree of the main throttle valve V1 such that an actualpressure detected by the intake pressure sensor 39 approaches the targetpressure.

If the engine load is greater than or equal to the specific value L1 andless than the specific value L2, the engine control device 73 refers toa first data table D1 storing the valve opening degree of the mainthrottle valve V1 with respect to the engine load and performs mapcontrol such that the valve opening degree of the main throttle valve V1reaches a degree corresponding to the engine load. The first data tableD1 is defined such that the valve opening degree of the main throttlevalve V1 gradually increases as the engine load increases.

If the engine load is greater than or equal to the specific value L2,the engine control device 73 performs control such that the mainthrottle valve V1 is fully open. The specific value L2 of the engineload is set to be lower than a value Lt at which the air pressure of theintake manifold 67 is an atmospheric pressure.

Then, control of the intake bypass valve V2 will be described withreference to FIG. 7(b).

If the engine load is less than the specific value L3, the enginecontrol device 73 performs control such that the intake bypass valve V2is fully closed.

If the engine load is greater than or equal to the specific value L3,the engine control device 73 sets a target pressure of the intakemanifold 67 in accordance with the engine load based on the relationshipshown in FIG. 7(d), and then performs PID control (feedback control) onthe valve opening degree of the intake bypass valve V2 such that anactual pressure detected by the intake pressure sensor 39 approaches thetarget pressure.

Next, control of the exhaust bypass valve V3 will be described withreference to FIG. 7(c).

If the engine load is less than the specific value L1, the enginecontrol device 73 performs control such that the exhaust bypass valve V3is fully open.

If the engine load is greater than or equal to the specific value L1,the engine control device 73 refers to a second data table D2 storingthe valve opening degree of the exhaust bypass valve V3 with respect tothe engine load and performs map control such that the valve openingdegree of the exhaust bypass valve V3 reaches the degree correspondingto the engine load. The second data table D2 is defined such that thevalve opening degree of the exhaust bypass valve V3 gradually decreasesas the engine load increases from the specific value L1 to the specificvalue L2, the exhaust bypass valve V3 is fully closed from the specificvalue L2 to the specific value L3, and the opening degree of the exhaustbypass valve V3 gradually increases as the engine load increases fromthe specific value L3.

As described above, the engine control device 73 adjusts the airpressure of the intake manifold 67 by controlling the main throttlevalve V1, the intake bypass valve V2, and the exhaust bypass valve V3.Accordingly, compressed air is supplied from the compressor 49 b to theintake manifold 67 so as to obtain an airflow rate necessary for anengine output, and an air-fuel ratio to fuel gas supplied from the gasinjectors 98 can be adjusted to a value in accordance with an engineoutput.

In the dual fuel engine as described in this embodiment, the air-fuelratio differs between the diesel mode and the gas mode. With the samelevel of a load, the required airflow rate in the gas mode is smallerthan that in the diesel mode. Thus, the turbocharger 49 basically needsto be designed to be used in the diesel mode, whereas in the gas mode,the turbocharger 49 also needs to supply air at a flow rate suitable forthe air-fuel ratio in the gas mode.

In this regard, in this embodiment, the configuration described abovecontrols the valve opening degree of the intake bypass valve V2 inaccordance with variations of the engine load during driving in the gasmode even in a case where the configuration of the turbocharger 49 isoptimized for driving in the diesel mode.

Accordingly, responsiveness in pressure control of the intake manifold67 can be enhanced. Thus, even when the load varies, excess anddeficiency of an air volume necessary for combustion can be avoided.Consequently, even when the turbocharger 49 optimized for driving in thediesel mode is used, the turbocharger 49 can be driven favorably in thegas mode.

The opening degree of the exhaust bypass valve V3 is controlled inaccordance with variations of the engine load so that air in an air-fuelratio necessary for combustion of fuel gas can be supplied to the engine21. In addition, control of the intake bypass valve V2 showing highresponsiveness is additionally performed so that response speed to aload variation can be increased in the gas mode. Thus, even with avariation of a load, problems such as knocking due to shortage of an airvolume necessary for combustion can be avoided.

Appropriate detection of an engine load is important for appropriatelycontrolling combustion of the engine 21. If the torque sensor 64 cannotdetect an engine load for some reasons, problems such as a decrease inoutput and degradation of fuel consumption can occur. In particular, inthe case of driving the dual fuel engine as described in this embodimentin the gas mode, to avoid knocking and accidental fire even at theoccurrence of load variation as described above, the engine load needsto be accurately detected for control of the airflow rate.

In this embodiment, the engine load is detected by the torque sensor 64illustrated in FIG. 6 in the range from 4 mA to 20 mA, for example, as asignal whose current value increases as the load increases. Thus, a casewhere the current value of the torque sensor 64 is 4 mA means that theengine load is substantially zero, but the possibility that the engineload is erroneously detected to be zero because of disconnection of thetorque sensor 64 or other reasons is not zero.

In this regard, in this embodiment, the engine control device 73calculates an illustrated mean effective pressure from a data sequenceobtained by detection of a cylinder internal pressure by the cylinderinternal pressure sensor 63. If the engine load detected value of thetorque sensor 64 shows no load although the obtained illustrated meaneffective pressure is greater than or equal to a predeterminedthreshold, it is determined that an abnormality occurs in detection ofan engine load by the torque sensor 64.

That is, if the cylinder internal pressure detected by the cylinderinternal pressure sensor 63 is a predetermined level or more, at least acertain level of a load is expected to be applied to the engine 21. Inspite of this, if the detection result of the engine load obtained bythe torque sensor 64 shows zero, it is highly possible that anabnormality occurs in detection of an engine load by the torque sensor64.

By using this determination, the engine control device 73 is configuredto determine that an abnormality occurs in the torque sensor 64 if theabove-described situation occurs, and to cause a display 72 of theengine-side operation control device 71 to display the occurrence ofabnormality. Accordingly, an abnormality in detection of an engine loadcan be appropriately found to promote early measures.

Next, specific control for detecting an abnormality in the torque sensor64 described above will be described in detail with reference mainly toFIG. 8. FIG. 8 is a flowchart depicting a determination processperformed by the engine control device 73 for detecting an abnormalityin the torque sensor 64. FIG. 9 is a view for describing control ofsupply of fuel gas and fuel oil in the case of switching from the gasmode to the diesel mode as a result of detection of an abnormality inthe torque sensor 64.

As illustrated in FIG. 8, in the engine 21 driven in the gas mode, theengine control device 73 performs control of adjusting the amount offuel gas injected by the gas injectors 98 such that the engine speeddetected by the engine speed sensor 65 approaches a target value (speedadjustment control, step S101).

Then, the engine control device 73 controls the opening degrees of themain throttle valve V1, the intake bypass valve V2, and the exhaustbypass valve V3 in accordance with the engine load detected by thetorque sensor 64 (step S102). As a method of control, one of the controlof fixing in a fully open state, the control of fixing in a fully closedstate, the map control, and the PID control (feedback control) isselected depending on the level of the engine load, as described withreference to FIG. 7.

Thereafter, the engine control device 73 determines whether the engineload obtained in step S102 is substantially no load or not (step S103).

In step S103, if it is determined that the detected engine load is notsubstantially zero, the process returns to step S101, and the process isrepeated.

In step S103, if it is determined that the detected engine load issubstantially zero, an illustrated mean effective pressure is calculatedfrom the pressure detected by the cylinder internal pressure sensor 63,and it is determined whether the illustrated mean effective pressure isgreater than or equal to a predetermined threshold or not (step S104).

In step S104, if it is determined that the illustrated mean effectivepressure is less than the threshold, the process returns to step S101,and the process is repeated.

In step S104, if it is determined that the illustrated mean effectivepressure is greater than or equal to the threshold, the engine controldevice 73 determines that an abnormality occurs in the torque sensor 64,and causes an the display 72 of the engine-side operation control device71 to show a message of occurrence of this abnormality. Accordingly, anoperator of the engine 21 finds occurrence of an abnormality indetection of an engine load early, and can take appropriate measures.

Subsequently, the engine control device 73 switches the combustion modeto the diesel mode (step S106), and the process in the gas mode isfinished. In this manner, when an abnormality occurs in detection of anengine load, the gas mode is switched to the diesel mode so thatoperation continuity required for a large-size engine for a ship can bethereby obtained.

In the dual fuel engine, switching from the gas mode to the diesel modemay be performed immediately or may be performed gradually.

For example, in a case where navigation of the ship causes the engine 21driven in the gas mode to travel out of a restricted area where theemission amount of nitrogen oxide and other substances is restricted,the gas mode is preferably gradually switched to the diesel mode. Inthis case, control is performed such that the amount of fuel gasinjected from the gas injectors 98 is gradually reduced or the amount ofliquid fuel injected from the main fuel injection valves 79 is graduallyincreased.

On the other hand, when an abnormality occurs during driving in the gasmode, the gas mode is preferably immediately switched to the dieselmode. Examples of possible abnormality include a decrease in pressure offuel gas, a decrease in pressure of the intake manifold 67, an increasein gas temperature, an increase in air temperature, and abnormalities ofsensors (including an abnormality in the torque sensor 64) describedabove. In this case, control is performed such that the amount of fuelgas injected from the gas injectors 98 is rapidly reduced to zero, andsubstantially at the same time, the amount of liquid fuel injected fromthe main fuel injection valve 79 is rapidly increased from zero.

In this embodiment, the switching from the gas mode to the diesel modeafter detection of occurrence of an abnormality in the torque sensor 64(step S106) is performed not gradually but instantaneously, as shown inFIG. 9.

In general, the amount of liquid fuel (main fuel) injected from the mainfuel injection valve 79 in the diesel mode can be obtained from anengine speed and an engine load with reference to a map. However, sincean abnormality occurs in the torque sensor 64 as described above, inobtaining an initial amount of injection of main fuel after switchingfrom the gas mode to the diesel mode in step S106 (fuel oil supplyamount FO1 in FIG. 9), the engine load detected by the torque sensor 64is unreliable. In view of this, the engine control device 73 isconfigured to obtain an illustrated mean effective pressure from thecylinder internal pressure detected by the cylinder internal pressuresensor 63, calculate a brake mean effective pressure (BMEP) from theunillustrated mean effective pressure, and estimate an engine load fromthe brake mean effective pressure. A relationship between theillustrated mean effective pressure and the brake mean effectivepressure and a relationship between the brake mean effective pressureand the engine load are well known, and thus, specific calculationthereof will not be described.

Subsequently, the engine control device 73 obtains an initial injectionamount of main fuel (fuel oil supply amount FO1 in FIG. 9) from the mapusing the engine speed and the estimated engine load, and controls thespeed adjuster 201 such that the obtained amount of liquid fuel isinjected from the main fuel injection valve 79. With this configuration,even in a situation where the engine load cannot be normally detected bythe torque sensor 64, an appropriate amount of liquid fuel can beinjected from the main fuel injection valve 79 immediately afterswitching to the diesel mode, and the engine speed can be favorablymaintained.

As described above, the engine 21 according to this embodiment includesthe cylinder internal pressure sensor 63, the torque sensor 64, and theengine control device 73. The cylinder internal pressure sensor 63detects the internal pressure of the cylinder. The torque sensor 64detects an engine load. The engine control device 73 receives adetection result of the cylinder internal pressure sensor 63 and adetection result of the torque sensor 64. If the load detected by thetorque sensor 64 is zero (no load) and the cylinder internal pressureobtained from the detection result of the cylinder internal pressuresensor 63 (specifically an illustrated mean effective pressure) isgreater than or equal to the threshold, the engine control device 73determines that an abnormality occurs in detection by the torque sensor64.

Accordingly, it is possible to determine whether an abnormality occursin the torque sensor 64 or not with a simple configuration by using acertain degree of correlation between the internal pressure of thecylinder and the engine load. Consequently, an operator can be urgedearly to cope with an abnormality, for example.

The engine 21 according to this embodiment includes the intake manifold67, the gas injectors 98, and the main fuel injection valve 79. Theintake manifold 67 supplies air into the cylinders. The gas injectors 98inject fuel gas to air supplied from the intake manifold 67 and mix theinjected fuel gas with the air. The main fuel injection valve 79 injectsliquid fuel into the cylinders. The engine 21 can be driven while beingswitched between the gas mode (premixed combustion mode) in whichgaseous fuel injected by the gas injectors 98 is mixed with air and thenthe mixture is caused to flow into the combustion chambers 110 of thecylinders and the diesel mode (diffusion combustion mode) in which themain fuel injection valves 79 inject liquid fuel into the combustionchambers 110. If it is determined that an abnormality occurs indetection by the torque sensor 64 during driving in the gas mode, theengine control device 73 switches the gas mode to the diesel mode.

Accordingly, it is possible to prevent driving of the engine 21 in thegas mode with occurrence of an abnormality in detection of an engineload by the torque sensor 64. As a result, continuity of driving of theengine 21 can be maintained.

In the engine 21 according to this embodiment, if it is determined thatan abnormality occurs in detection by the torque sensor 64 duringdriving in the gas mode and the gas mode is switched to the diesel mode,the engine control device 73 estimates an engine load by calculationbased on a detection value of the cylinder internal pressure sensor 63,and based on the estimated engine load, calculates the amount of liquidfuel injected by the main fuel injection valves 79 immediately afterswitching to the diesel mode.

Accordingly, in an initial stage in which the gas mode is switched tothe diesel mode, an appropriate amount of liquid fuel can be injectedform the main fuel injection valves 79. Consequently, the engine 21 canbe driven stably without degradation of the engine speed in modeswitching, for example.

The foregoing description is directed to the preferred embodiment of thepresent invention, and the configuration described above may be changed,for example, as follows.

The torque sensor 64 may be configured to output a signal of a voltagevalue in accordance with an engine load, for example, instead ofoutputting a signal of a current value in accordance with the engineload.

In S104 in the flowchart of FIG. 8, not the illustrated mean effectivepressure (IMEP) but the brake mean effective pressure (BMEP), forexample, may be compared with the threshold.

The load detector is not limited to the torque sensor 64 describedabove, and may be a watt transducer, for example.

In the embodiment described above, ignition of premixed gas in the gasmode is performed by injecting a small amount of liquid fuel from thepilot fuel injection valves 82 (micro pilot ignition). Instead of this,ignition by a spark, for example, may be performed.

In the embodiment described above, the engine 21 is used as a drivingsource of a propulsive and power generating mechanism of a ship, butthis is not restrictive, and the engine 21 may be used for otherpurposes.

REFERENCE SIGNS LIST

-   -   21 engine    -   24 crank shaft    -   64 cylinder internal pressure sensor    -   78 torque sensor (load detector)    -   78 engine control device (control device)    -   79 piston    -   79 main fuel injection valve (fuel injection valve)    -   80 98 gas injector    -   81 110 combustion chamber

1-3: (canceled) 4: An engine comprising: a gas injector that injectsgaseous fuel; a main fuel injection valve that injects liquid fuel; anda control device for switching between a gas mode in which the gaseousfuel injected from the gas injector and mixed with air is caused to flowinto a combustion chamber and a diesel mode in which combustion occursby injection of the liquid fuel by the main fuel injection valve intothe combustion chamber, wherein if it is determined that an abnormalityhas occurred within the engine, the control device controls to switch tothe diesel mode. 5: The engine according to claim 4, wherein the controldevice determines the amount of the liquid fuel supplied after switchingto the diesel mode based on engine speed and engine load.